Fiber-reinforced resin composite material

ABSTRACT

The resin-reinforcing fiber of the preset invention is a fiber surface-treated with an epoxidized polydiene resin. The fiber is preferably carbon fiber or glass fiber. The fiber-reinforced resin composite material of the present invention comprises the resin-reinforcing fiber and a matrix resin. The matrix resin is preferably an epoxy thermosetting resin. 
     The resin-reinforcing fiber of the present invention can improve the absorbed energy up to the maximum load (elastic energy) of a fiber-reinforced resin composite material and the absorbed energy after the maximum load (propagation energy) thereof at the same time.

TECHNICAL FIELD

The present invention relates to a resin-reinforcing fiber useful for producing a fiber-reinforced composite material, a fiber-reinforced resin composite material using the resin-reinforcing fiber, and a structure comprising the fiber-reinforced resin composite material.

BACKGROUND ART

A fiber-reinforced resin composite material is a composite material comprising reinforcing fibers and a matrix resin, and is widely used in the fields of automobile parts, products for civil engineering and construction, blades for wind power generation, sporting goods, aircraft, ships, robots, cable materials, and the like. Glass fiber, aramid fiber, carbon fiber, boron fiber, and the like are used as the reinforcing fibers. A thermosetting resin with which the reinforcing fibers are easily impregnated is frequently used as the matrix resin. Epoxy resin, unsaturated polyester resin, vinyl ester resin, phenolic resin, maleimide resin, cyanate resin, and the like are used as the thermosetting resin, and among them, epoxy resin, which has excellent heat resistance, modulus of elasticity, and chemical resistance, and small cure shrinkage, is most frequently used.

To provide a carbon fiber-reinforced resin composite material excellent in impact resistance, Japanese Patent No. 3136883 (Patent Literature 1) discloses a carbon fiber-reinforced resin composite material reinforced with carbon fiber, wherein the carbon fiber has a specific gravity of 1.75 or less, has specific values or more of tensile modulus of elasticity and tensile strength, has a surface nitrogen concentration N/C and a surface oxygen concentration O/C in specific ranges, is treated with 0.01 to 5% of an epoxy sizing agent comprising an aliphatic compound having a plurality of epoxy groups per unit weight of the carbon fiber, and has an edge delamination strength of 22 kgf/mm² or more. An aliphatic compound having a number of epoxy groups of 2 to 4 and a molecular weight of 100 to 2000 is used as the epoxy sizing agent.

To provide a carbon fiber to which a sizing agent has adhered, wherein the carbon fiber has small variation in adhesive strength; the adhesive strength between the carbon fiber and a matrix resin is improved; and the carbon fiber can stably provide a composite material having excellent mechanical properties, Japanese Patent No. 3003521 (Patent Literature 2) discloses a carbon fiber to which a sizing agent comprising bisphenol A diglycidyl ether or an aliphatic compound having a plurality of epoxy groups has adhered, wherein the thickness of the sizing agent is within a specific range, and the ratio of the maximum value of the thickness of the sizing agent to the minimum value thereof is within a specific range.

CITATION LIST Patent Literature

-   Patent Literature 1: Japanese Patent No. 3136883 -   Patent Literature 2: Japanese Patent No. 3003521

SUMMARY OF INVENTION Technical Problem

However, it is difficult to sufficiently increase the adhesiveness between reinforcing fibers and a matrix resin because, with regard to the reinforcing fibers described in the above literatures, the number of epoxy groups in the molecules of the sizing agent to be adhered to the fibers is small, and the molecular weight of the sizing agent is also small. Furthermore, with respect to the impact resistance of a fiber-reinforced resin composite material, it has conventionally been difficult to improve the absorbed energy up to the maximum load (elastic energy) and the absorbed energy after the maximum load (propagation energy) thereof at the same time. That is, when it is intended to increase the absorbed energy up to the maximum load by increasing the adhesiveness between fibers and a matrix resin, the absorbed energy after the maximum load will be reduced, and, conversely, when it is intended to increase the absorbed energy after the maximum load, the absorbed energy up to the maximum load will be reduced. Thus, there is a tradeoff between the absorbed energy up to the maximum load and the absorbed energy after the maximum load.

An object of the present invention is to provide a resin-reinforcing fiber capable of improving the absorbed energy up to the maximum load (elastic energy) of a fiber-reinforced resin composite material and the absorbed energy after the maximum load (propagation energy) thereof at the same time, a fiber-reinforced resin composite material using the resin-reinforcing fiber, and a structure comprising the fiber-reinforced resin composite material.

Solution to Problem

As a result of extensive studies for achieving the above object, the present inventors have found that when a fiber surface-treated with an epoxidized polydiene resin is used as a reinforcing fiber, the absorbed energy up to the maximum load of a fiber-reinforced resin composite material and the absorbed energy after the maximum load thereof can be improved at the same time, and have completed the present invention.

Specifically, the present invention provides a resin-reinforcing fiber in which a fiber is surface-treated with an epoxidized polydiene resin.

The fiber is preferably carbon fiber or glass fiber.

The present invention also provides a fiber-reinforced resin composite material comprising the resin-reinforcing fiber and a matrix resin.

The matrix resin is preferably an epoxy thermosetting resin.

The present invention further provides a structure comprising the fiber-reinforced resin composite material.

Advantageous Effects of Invention

In the resin-reinforcing fiber of the present invention, the surface of the fiber is treated with an epoxidized polydiene resin having rubber elasticity in the molecular main chain itself and having many epoxy groups in the molecule, and, therefore, in a fiber-reinforced resin composite material using the fiber as a reinforcing fiber, an interphase which has extremely high adhesion (adhesiveness) to the matrix resin and is significantly excellent in flexibility is formed between the fiber and a matrix resin. Thus, the absorbed energy up to the maximum load (elastic energy) of the fiber-reinforced resin composite material and the absorbed energy after the maximum load (propagation energy) thereof can be improved at the same time. That is, although it has been difficult to achieve compatibility between dynamic strength and static strength, it has now become possible to improve dynamic strength and static strength at the same time. Therefore, although a fiber-reinforced resin composite material which is strong against an instantaneous impact generally had a disadvantage of being brittle after having been subjected to impact, the fiber-reinforced resin composite material of the present invention has toughness, and it can not only endure a strong impact, but can keep high strength even after it is subjected to the strong impact.

DESCRIPTION OF EMBODIMENTS Resin-Reinforcing Fiber

The resin-reinforcing fiber of the present invention is a fiber surface-treated with an epoxidized polydiene resin. A fiber which is generally used for a fiber-reinforced resin composite material can be used without particular limitation, and examples thereof include carbon fiber, glass fiber, aramid fiber, and boron fiber. Among these, carbon fiber and glass fiber are particularly preferred. The fiber can be used alone or in combination of two or more thereof.

Examples of the carbon fiber which can be used include polyacrylonitrile (PAN)-based carbon fiber, pitch-based carbon fiber, and vapor-grown carbon fiber. As the glass fiber, a glass fiber generally used for resin reinforcement can be used.

Examples of the epoxidized polydiene resin which can be used include epoxidized products of polybutadiene, polyisoprene, and a copolymer of a compound having a butadiene structure or an isoprene structure in the molecule. Examples of the epoxidized products of a copolymer of a compound having a butadiene structure or an isoprene structure in the molecule include an epoxidized product of a copolymerized polyene having a butadiene structure (for example, an epoxidized product of styrene/butadiene/styrene copolymer) and an epoxidized product of a copolymerized polyene having an isoprene structure (for example, an epoxidized product of styrene/isoprene/styrene copolymer). A terminal group of the polybutadiene, polyisoprene, and copolymer of a compound having a butadiene structure or an isoprene structure in the molecule may be a hydrogen atom, a hydroxy group, a cyano group, or the like. Particularly, a hydrogen atom and a hydroxy group are preferred as a terminal group. Among the epoxidized polydiene resins, epoxidized polybutadiene, epoxidized polyisoprene, an epoxidized styrene/butadiene/styrene copolymer, and an epoxidized styrene/isoprene/styrene copolymer are preferred, and epoxidized polybutadiene is particularly preferred. The epoxidized polydiene resin can be used alone or in combination of two or more thereof.

The epoxidized polydiene resin can be obtained by allowing an epoxidizing agent to react with polybutadiene, polyisoprene, or a copolymer of a compound having a butadiene structure or an isoprene structure in the molecule.

In the polybutadiene, polyisoprene, or copolymer of a compound having a butadiene structure or an isoprene structure in the molecule which is a raw material, the configuration of a double bond part may be any of cis-1,4, trans-1,4, trans-1,2, and cis-1,2. Furthermore, the ratio thereof may be arbitrary.

Examples of the epoxidizing agent include organic peracids such as peracetic acid, performic acid, perbenzoic acid, trifluoroperacetic acid, and perpropionic acid, hydrogen peroxide, and organic hydroperoxides such as t-butyl hydroperoxide and cumene hydroperoxide. In order to increase the oxirane oxygen concentration of an object, an organic peracid which does not substantially contain water (for example, having a water content of 0.8% by weight or less) is preferred. Among the above epoxidizing agents, peracetic acid is particularly preferred in that it can be obtained industrially inexpensively and has a high degree of stability.

A catalyst can be used for epoxidation. When an organic peracid is used as an epoxidizing agent, an alkali such as sodium carbonate and an acid such as sulfuric acid can be used as a catalyst. Further, when hydrogen peroxide is used as an epoxidizing agent, an organic acid and a mixture of tungstic acid and sodium hydroxide can be used as a catalyst. Furthermore, when an organic hydroperoxide such as t-butyl hydroperoxide is used, molybdenum hexacarbonyl can be used as a catalyst.

The epoxidation reaction can be performed in an inert solvent. Examples of the inert solvent include aliphatic hydrocarbons such as hexane and heptane; alicyclic hydrocarbons such as cyclohexane; aromatic hydrocarbons such as benzene, toluene, and xylene; ethers; esters such as ethyl acetate; halogenated hydrocarbons such as chloroform and carbon tetrachloride; and mixed solvents thereof.

The reaction temperature of epoxidation can be suitably selected depending on the type of an epoxidizing agent. When peracetic acid is used as an epoxidizing agent, reaction temperature is, for example, 20 to 80° C. When t-hydroperoxide is used as an epoxidizing agent, reaction temperature is, for example, 20 to 150° C.

The charging molar ratio of an epoxidizing agent to a raw material (polybutadiene, polyisoprene, or a copolymer of a compound having a butadiene structure or an isoprene structure in the molecule) can be suitably selected depending on a target degree of epoxidation. It is preferred to add 1 to 2 mol of the epoxidizing agent to 1 mol of double bonds which the raw material has.

The produced epoxidized polydiene resin can be isolated by a suitable method, for example, a method of precipitating the resin with a poor solvent, a method of putting a polymer in hot water with stirring and removing a solvent by distillation, a method of directly deliquoring, and the like.

The number average molecular weight of the epoxidized polydiene resin is, for example, 500 to 50000, preferably 2500 to 30000, more preferably 3500 to 20000. The oxirane oxygen concentration of the epoxidized polydiene resin is, for example, 3 to 15%, preferably 5 to 12%. The number of epoxy groups in one molecule is preferably 5 or more (for example, 5 to 200), more preferably 10 or more, further preferably 20 or more.

[Preparation of Resin-Reinforcing Fiber]

The resin-reinforcing fiber of the present invention can be obtained by subjecting a fiber to surface treatment with an epoxidized polydiene resin. The form of the fibers is not particularly limited, and examples thereof may include any form such as single fiber, yarn, strands, woven fabrics, knits, mats, and braids. A method of the surface treatment which can be used is not particularly limited, and examples thereof may include a method of immersing fibers in a solution or dispersion of the epoxidized polydiene resin or spraying fibers with a solution or dispersion of the epoxidized polydiene resin to adhere the epoxidized polydiene resin to the surface of the fibers. After the operation of immersion, spraying, or the like, the surface-treated fibers are dried at a suitable temperature to remove a solvent. The drying temperature can be suitably selected according to the type of solvent and the like, and is, for example, about 35 to 350° C., preferably 40 to 250° C.

Examples of the solvent used for the preparation of a solution or dispersion of the epoxidized polydiene resin include water; alcohols such as methanol and ethanol; amides or lactams such as dimethylformamide and dimethylacetamide; ketones such as acetone; esters or lactones; and mixed solutions thereof.

A surfactant, an emulsifier, a dispersing agent, and the like can be used for the preparation of a solution or dispersion of the epoxidized polydiene resin, if needed (particularly, when water is used as a solvent). As a surfactant, any of an anionic surfactant, a nonionic surfactant, a cationic surfactant, and the like may be used. A surfactant, an emulsifier, a dispersing agent, and the like can be used alone or in combination of two or more thereof. A dispersion in which the epoxidized polydiene resin is encapsulated and emulsified can also be used for the surface treatment of the fibers.

In the resin-reinforcing fiber, the treatment amount (adhesion amount) of the epoxidized polydiene resin is, for example, 0.01 to 5 parts by weight, preferably 0.1 to 4 parts by weight, more preferably 0.3 to 3 parts by weight, relative to 100 parts by weight of fiber. If this amount is too small, the adhesion between a fiber and a matrix resin will tend to be lower in the production of a fiber-reinforced resin composite material, and if it is too large, a thick layer of a cured product of the epoxidized polydiene resin will be present between a fiber and a matrix resin, which may change the properties of the composite material.

[Fiber-Reinforced Resin Composite Material]

The fiber-reinforced resin composite material of the present invention comprises the resin-reinforcing fiber and a matrix resin. The matrix resin may be any of a thermosetting resin and a thermoplastic resin, but a thermosetting resin is preferred in that it is easily impregnated into reinforcing fibers. Examples of the thermosetting resin which is used include an epoxy resin, an unsaturated polyester resin, a vinyl ester resin, a phenolic resin, a maleimide resin, and a cyanate resin. Among the above resins, the matrix resin is preferably an epoxy thermosetting resin in that it is excellent in heat resistance, a modulus of elasticity, and chemical resistance, and has small cure shrinkage.

The epoxy thermosetting resin is not particularly limited, but an epoxy compound having two or more epoxy groups in the molecule is preferred as an epoxy compound before curing. The epoxy compound can be used alone or in combination of two or more thereof.

The epoxy compound having two or more epoxy groups in the molecule is not particularly limited, and examples thereof which can be used include an alicyclic epoxy compound, a bisphenol-type diepoxy compound, an aliphatic polyhydric alcohol polyglycidyl ether, and a polyglycidyl amine-type epoxy resin.

The alicyclic epoxy compound is not particularly limited as long as it is a compound having an alicyclic skeleton and two or more epoxy groups in the molecule, but is preferably (i) an epoxy compound having two or more alicyclic epoxy groups in which an epoxy group is formed including two adjacent carbon atoms constituting the alicyclic skeleton is preferred. Such an alicyclic epoxy compound includes a compound represented by the following formula (1):

The alicyclic epoxy compound represented by the above formula (1) is produced by oxidizing the corresponding alicyclic olefin compound with an aliphatic percarboxylic acid or the like, and an alicyclic epoxy compound produced by using a substantially anhydrous aliphatic percarboxylic acid is preferred in terms of having a high epoxidation rate.

In the above formula (1), Y represents a single bond or a linking group. Examples of the linking group include a divalent hydrocarbon group, a carbonyl group (—CO—), an ether bond (—O—), an ester bond (—COO—), an amide bond (—CONH—), a carbonate bond (—OCOO—), and a group in which a plurality of them are linked. Preferred examples of the divalent hydrocarbon group include a linear or branched alkylene group having 1 to 18 (particularly, 1 to 6) carbon atoms and a divalent alicyclic hydrocarbon group (particularly, a divalent cycloalkylene group). Examples of the linear or branched alkylene group include a methylene, methylmethylene, dimethylmethylene, ethylene, propylene, and trimethylene group. Furthermore, examples of the divalent alicyclic hydrocarbon group include a 1,2-cyclopentylene, 1,3-cyclopentylene, cyclopentylidene, 1,2-cyclohexylene, 1,3-cyclohexylene, 1,4-cyclohexylene, and cyclohexylidene group.

Specific examples of the alicyclic epoxy compound represented by formula (1) include the following compounds.

In the above formula, n is an integer of 1 to 30.

In addition to the above (i), the following compounds can also be used as the alicyclic epoxy compound: (ii) an epoxy compound in which only one of the two epoxy groups is the alicyclic epoxy group which is formed including two adjacent carbon atoms constituting the alicyclic skeleton (for example, limonene diepoxide); (iii) an epoxy compound in which a carbon atom constituting the epoxy group is bonded to a carbon atom constituting the alicyclic skeleton by a single bond; and (iv) a glycidyl ether compound (for example, a glycidyl ether-type epoxy compound having an alicyclic skeleton and a glycidyl ether group). Specific examples of the above-described compounds include the following compounds.

In the above formula, R represents a group obtained by removing q OHs from a q-valent alcohol [R—(OH)_(q)]; p represents an integer of 1 to 50; and q represents an integer of 1 to 10. In the groups in q parentheses, each p may be the same or different. Examples of the q-valent alcohol [R—(OH)_(q)] include monovalent alcohols such as methanol, ethanol, 1-propanol, isopropyl alcohol, and 1-butanol; divalent alcohols such as ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, neopentyl glycol, 1,6-hexanediol, diethylene glycol, triethylene glycol, tetraethylene glycol, dipropylene glycol, and polypropylene glycol; and trivalent or more alcohols such as glycerin, diglycerin, erythritol, trimethylolethane, trimethylolpropane, pentaerythritol, dipentaerythritol, and sorbitol. The alcohol may be polyether polyol, polyester polyol, polycarbonate polyol, polyolefin polyol, and the like. The alcohol is preferably an aliphatic alcohol having 1 to 10 carbon atoms (particularly, an aliphatic polyhydric alcohol such as trimethylolpropane).

In addition, it is also possible to use (v) a polyfunctional epoxy compound having 3 or more epoxy groups. Specific examples include the following compounds.

In the above formulas, a, b, c, d, e, and f represent integers of 0 to 30.

A known compound can be used as the bisphenol-type diepoxy compound, and examples thereof include a bisphenol A-type epoxy resin (bisphenol A diglycidyl ether; a condensation product of bisphenol A and epichlorohydrin, having glycidyl ether groups at both ends; and the like), a bisphenol F-type epoxy resin (bisphenol F diglycidyl ether; a condensation product of bisphenol F and epichlorohydrin, having glycidyl ether groups at both ends; and the like), and a bisphenol S-type epoxy resin (bisphenol S diglycidyl ether; a condensation product of bisphenol S and epichlorohydrin, having glycidyl ether groups at both ends; and the like).

The aliphatic polyhydric alcohol polyglycidyl ether is not particularly limited. Examples of the “aliphatic polyhydric alcohol” in the aliphatic polyhydric alcohol polyglycidyl ether include divalent alcohols such as ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, neopentyl glycol, 1,6-hexanediol, diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, dipropylene glycol, and polypropylene glycol; and trivalent or more alcohols such as glycerin, diglycerin, polyglycerin, erythritol, trimethylolethane, trimethylolpropane, pentaerythritol, and dipentaerythritol.

Representative examples of the aliphatic polyhydric alcohol polyglycidyl ether include 1,6-hexanediol diglycidyl ether, 1,4-butanediol diglycidyl ether, trimethylolpropane polyglycidyl ether, diethylene glycol diglycidyl ether, neopentyl glycol diglycidyl ether, propylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, and polyethylene glycol diglycidyl ether.

Examples of the polyglycidyl amine-type epoxy resin include N,N,N′,N′-tetraglycidyl-4,4′-methylene-bisbenzamine.

The epoxy compound is preferably liquid in terms of improving the workability during the formulation and the production of the fiber-reinforced resin composite material. However, even if the epoxy compound is solid in itself, it can be used if the viscosity (25° C.) of a curable composition after blending each component is, for example, 20000 mPa·s or less. The viscosity (25° C.) of the epoxy compound (a mixture of all the epoxy compounds to be used) is, for example, 50000 mPa·s or less, preferably 30000 mPa·s or less, more preferably 20000 mPa·s or less. If the viscosity is too high, workability and the like will tend to be reduced.

[Production of Fiber-Reinforced Resin Composite Material]

When the matrix resin is a thermosetting resin, the fiber-reinforced resin composite material of the present invention can be produced by curing a mixed material comprising the resin-reinforcing fiber of the present invention and a curable composition (composition before curing) for forming the matrix resin. The curing is generally performed by heating. A known method can be applied to the production of the fiber-reinforced resin composite material, and examples thereof include a prepreg method, a hand lay-up method, a filament winding method, an RTM (Resin Transfer Molding) method, a pultrusion method, and a vacuum infusion method.

Generally, the curable composition comprises a curable compound (epoxy compound or the like), a curing agent and a curing accelerator, or a curing catalyst, and various additives optionally blended.

The curing agent is not particularly limited, but can be suitably selected depending on the type or the like of the curable compound. When the curable compound is an epoxy compound or the like, an acid anhydride, a polyamine, and the like are preferably used as a curing agent. The curing agent can be used alone or in combination of two or more thereof.

The acid anhydride can be arbitrarily selected and used from among those conventionally used as a curing agent for epoxy resins. The acid anhydride is preferably liquid at normal temperature, and specific examples thereof include methyltetrahydrophthalic anhydride, a methylhexahydrophthalic anhydride, dodecenyl succinic anhydride, and methyl-endomethylene tetrahydrophthalic anhydride. Furthermore, an acid anhydride which is solid at normal temperature, for example, phthalic anhydride, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, and methylcyclohexenedicarboxylic anhydride can be used in the range that does not adversely affect the impregnating ability of the epoxy resin composition. When an acid anhydride which is solid at normal temperature is used, it is preferably dissolved in an acid anhydride which is liquid at normal temperature and used as a liquid mixture at normal temperature. Commercially available products such as trade name “RIKACID MH-700” (manufactured by New Japan Chemical Co., Ltd.), trade name “RIKACID MH” (manufactured by New Japan Chemical Co., Ltd.), and trade name “HN-5500” (manufactured by Hitachi Chemical Co., Ltd.) can also be used as the acid anhydride curing agent.

The polyamine can be arbitrarily selected and used from among those conventionally used as a curing agent for epoxy resins. A polyamine which is liquid at normal temperature is preferred. When a polyamine which is solid at normal temperature is used, it is preferably dissolved in a polyamine which is liquid at normal temperature and used as a liquid mixture at normal temperature. Specific examples of the polyamine include open-chain aliphatic polyamines such as diethylenetriamine, triethylenetetramine, tetraethylenepentamine, dipropylenediamine, and diethylaminopropylamine; cyclic aliphatic polyamines such as N-aminoethyl piperazine, menthenediamine, and isophoronediamine; and polyether polyamine [for example, trade name “JEFFAMINE D-230”, “JEFFAMINE D-400”, “JEFFAMINE D-2000”, “JEFFAMINE D-4000”, “JEFFAMINE ED-600”, “JEFFAMINE ED-900”, “JEFFAMINE ED-2003”, “JEFFAMINE EDR-148”, “JEFFAMINE EDR-176”, “JEFFAMINE T-403”, “JEFFAMINE T-3000”, “JEFFAMINE T-5000” (these are manufactured by Huntsman Corporation)].

The blending amount of the curing agent such as an acid anhydride curing agent and a polyamine curing agent is preferably used in an effective amount that can exhibit the effect as a curing agent, that is, in a proportion in which the acid anhydride equivalent (or the amine equivalent or the like) is 0.5 to 1.5 per 1 equivalent of epoxy groups in the epoxy compound in the epoxy resin composition.

The curing accelerator is not particularly limited as long as it is a curing accelerator generally used for the acceleration of the curing of an epoxy compound or the like, and examples thereof which can be used include tertiary amines, tertiary amine salts, imidazoles, organophosphorus compounds, quaternary ammonium salts, quaternary phosphonium salts, organometallic salts, and boron compounds. The curing accelerator can be used alone or in combination of two or more thereof.

Examples of the tertiary amines include lauryldimethylamine, N,N-dimethylcyclohexylamine, N,N-dimethylbenzylamine, N,N-dimethylaniline, (N,N-dimethylaminomethyl)phenol, 2,4,6-tris(N,N-dimethylaminomethyl)phenol, 1,8-diazabicyclo[5.4.0]undecene-7 (DBU), and 1,5-diazabicyclo[4.3.0]nonene-5 (DBN).

Examples of the tertiary amine salts include carboxylates, sulfonates, and inorganic acid salts of the tertiary amines. The carboxylates include salts of carboxylic acids having 1 to 30 carbon atoms (particularly, 1 to 10 carbon atoms) (particularly, salts of fatty acid) such as octylic acid salts. The sulfonates include p-toluenesulfonic acid salts, benzenesulfonic acid salts, methanesulfonic acid salts, and ethanesulfonic acid salts. Representative examples of the tertiary amine salts include salts (for example, p-toluenesulfonic acid salts and octylic acid salts) of 1,8-diazabicyclo[5.4.0]undecene-7 (DBU).

Examples of the imidazoles include 2-methylimidazole, 2-ethylimidazole, 1,2-dimethylimidazole, 2-ethyl-4-methylimidazole, 2-phenylimidazole, 2-phenyl-4-methylimidazole, and 1-benzyl-2-methylimidazole.

Examples of the organophosphorus compounds include triphenylphosphine and phosphorous acid triphenyl.

Examples of the quaternary ammonium salts include tetraethylammonium bromide and tetrabutylammonium bromide.

Examples of the quaternary phosphonium salts include tetrabutylphosphonium decanoate, tetrabutylphosphonium laurate, tetrabutylphosphonium myristate, tetrabutylphosphonium palmitate, a salt of a tetrabutylphosphonium cation and an anion of bicyclo[2.2.1]heptane-2,3-dicarboxylic acid and/or methylbicyclo[2.2.1]heptane-2,3-dicarboxylic acid, a salt of a tetrabutylphosphonium cation and an anion of 1,2,4,5-cyclohexane tetracarboxylic acid, a salt of a tetrabutylphosphonium cation and an anion of methanesulfonic acid, a salt of a tetrabutylphosphonium cation and an anion of benzenesulfonic acid, a salt of a tetrabutylphosphonium cation and an anion of p-toluenesulfonic acid, a salt of a tetrabutylphosphonium cation and an anion of 4-chlorobenzenesulfonic acid, and a salt of a tetrabutylphosphonium cation and an anion of dodecylbenzenesulfonic acid.

Examples of the organometallic salts include tin octylate, zinc octylate, dibutyltin dilaurate, and an aluminum acetylacetone complex.

Examples of the boron compounds include boron trifluoride and triphenyl borate.

Commercially available products such as trade names “U-CAT SA-506”, “U-CAT SA-102”, and “U-CAT 5003” (these are manufactured by San-Apro Ltd.) can also be used as a curing accelerator.

The blending amount of the curing accelerator is different depending on the type of the curing agent (acid anhydride curing agent and the like), but it is generally 0.01 to 15 parts by weight, preferably 0.1 to 10 parts by weight, more preferably 0.5 to 8 parts by weight relative to 100 parts by weight of the curing agent.

A cationic initiator, for example, can be used as a curing catalyst. The cationic initiator is an initiator which releases a substance for starting cationic polymerization by heating. Examples of the cationic initiator include aryl diazonium salts [for example, PP-33 (manufactured by ADEKA Corporation)], aryl iodonium salts, and aryl sulfonium salts [for example, FC-509 (manufactured by 3M Company), UVE1014 (manufactured by G.E. Company), CP-66, CP-77 (these are manufactured by ADEKA Corporation), and SI-60L, SI-80L, SI-100L, SI-110L (these are manufactured by Sanshin Chemical Industry Co., Ltd.)].

The amount of the curing catalyst used is, for example, 0.01 to 15 parts by weight, preferably 0.05 to 12 parts by weight, more preferably 0.1 to 10 parts by weight, relative to 100 parts by weight of the curable compound (epoxy compound or the like).

Examples of the various additives include a low molecular weight compound having a hydroxy group. The curing reaction can be slowly progressed by blending the low-molecular compound having a hydroxy group. Examples of the compound having a hydroxy group include polyhydric alcohols such as ethylene glycol, diethylene glycol, and glycerin.

In addition to the above, various types of additives can be blended with the curable composition in the range that does not adversely affect the physical properties of the cured product (fiber-reinforced resin composite material). Examples of such additives include a surfactant, an internal release agent, a coloring agent, flame retardant, a defoaming agent, a silane coupling agent, a filler, an antioxidant, and an ultraviolet absorber. The blending amount of these various types of additives is preferably 10% or less (particularly, 5% or less) by weight of the curable composition.

The curing temperature of the curable composition is different depending on the type of the curable compound, but it is, for example, 40 to 250° C., preferably 80 to 200° C.

The glass transition temperature of the fiber-reinforced resin composite material (cured product) obtained in this way is 90° C. or more, preferably 120° C. or more.

The volume fraction of fibers (Vf) in the fiber-reinforced resin composite material is different depending on applications, but it is generally 20 to 80%, preferably 35 to 70%.

The fiber-reinforced resin composite material of the present invention has both improved elastic energy and improved propagation energy and is not only strong against an impact but keeps the strength after the impact, and, therefore, it can be suitably used for a structure such as a body, wing, tail, moving blade, fairing, cowling, door, and the like of an aircraft, a motor case, wing, and the like of a spacecraft, a structure of an artificial satellite, an automobile part such as a chassis of a motor vehicle, a structure of a railway rolling stock, a structure of a bicycle, a structure of a ship, a blade for wind power generation, a pressure vessel, a fishing rod, a tennis racket, a golf shaft, a robot arm, and a cable.

EXAMPLES

Hereinafter, the present invention will be specifically described with reference to Examples, but the present invention is not limited to these.

Example 1

Carbon fiber cloth [manufactured by Toray Industries, Inc., a plain woven fabric of carbon fiber T700] was immersed in a solution in which 2 parts by weight of epoxidized polybutadiene [manufactured by Daicel Chemical Industries, Ltd., trade name “EPOLEAD PB3600”, oxirane oxygen concentration: 7.8%, number average molecular weight: 5900] was dissolved in 100 parts by weight of acetone for about 10 seconds, removed from the solution, and dried for 30 minutes at a temperature of 60° C. in a dryer. The weight of the carbon fiber cloth after drying increased by 1.5% compared with that before immersion, and, thus, it was verified that the epoxidized polybutadiene was applied to the carbon fiber.

Next, a single-layer body or a 12-layer laminate of the carbon fiber cloth after immersion and drying was impregnated, by a hand lay-up method, with a mixed solution (curable composition) obtained by mixing 100 parts by weight of 3,4-epoxycyclohexylmethyl(3,4-epoxy) cyclohexane carboxylate [manufactured by Daicel Chemical Industries, Ltd., trade name “CELLOXIDE 2021P”], 130 parts by weight of a mixture of 4-methylhexahydrophthalic anhydride and hexahydrophthalic anhydride [manufactured by New Japan Chemical Co., Ltd., trade name “RIKACID MH-700”], 0.65 part by weight of ethylene glycol, and 0.65 part by weight of an octylic acid salt of 1,8-diazabicyclo[5.4.0]undecene-7 [manufactured by San-Apro Ltd., trade name “SA-102”] as a curing accelerator, and the curable composition was cured in a heating oven at 110° C. for 2 hours and then further cured at 170° C. for 2 hours to obtain a carbon fiber-reinforced resin.

The volume fraction of fibers (Vf) of the obtained carbon fiber-reinforced resin was measured to be 54.0% for the single-layer body and 60.9% for the 12-layer laminate.

Comparative Example 1

The carbon fiber-reinforced resin having a single-layer body structure and that having a 12-layer laminate structure were produced in the same manner as in Example 1 except that the operation of immersing the carbon fiber cloth in the solution of epoxidized polybutadiene was not performed.

The volume fraction of fibers (Vf) of the obtained carbon fiber-reinforced resin was measured to be 54.0% for the single-layer body and 64.3% for the 12-layer laminate.

Evaluation Test 1

The carbon fiber-reinforced resins each having a single-layer body structure obtained in Example 1 and Comparative Example 1 were subjected to a tensile test to measure the modulus of elasticity (GPa) and tensile strength (MPa). The tensile test was performed according to the method of JIS K7073. Note that the test piece size of the single-layer body is 200 mm in length, 20 mm in width, and 0.35 mm in thickness. The results are shown in Table 1. In Table 1, the rate of increase was determined by the following formula.

Rate of increase (%)=[(value in Example 1−value in Comparative Example 1)/value in Comparative Example 1]×100

Evaluation Test 2

The carbon fiber-reinforced resins each having a 12-layer laminated structure obtained in Example 1 and Comparative Example 1 were subjected to a falling weight impact test to measure the absorbed energy up to the maximum load (elastic energy) and the absorbed energy after the maximum load (propagation energy). The falling weight impact test was performed according to the method of JIS K7085. Note that the test piece size of the 12-layer laminate was 100 mm in length, 100 mm in width, and 2 mm in thickness. The results are shown in Table 2. In Table 2, the rate of increase was determined by the following formula.

Rate of increase (%)=[(value in Example 1−value in Comparative Example 1)/value in Comparative Example 1]×100

TABLE 1 Modulus of Tensile elasticity strength Vf (GPa) (MPa) (%) Comparative 31.1 337 54.0 Example 1 Example 1 32.9 401 54.0 Rate of 5.8 19.0 increase (%)

TABLE 2 Elastic Propagation Total absorbed Vf energy (J) energy (J) energy (J) (%) Comparative 4.51 8.01 12.5 64.3 Example 1 Example 1 5.40 8.28 13.7 60.9 Rate of 19.7 3.37 9.60 increase (%)

Tables 1 and 2 show that the composite material using a resin-reinforcing fiber surface-treated with an epoxidized polydiene resin (Example 1) has significantly improved tensile strength and is increased in both elastic energy and propagation energy as compared with the composite material using a resin-reinforcing fiber which is not surface-treated with an epoxidized polydiene resin (Comparative Example 1).

INDUSTRIAL APPLICABILITY

The resin-reinforcing fiber of the present invention can improve the absorbed energy up to the maximum load (elastic energy) of a fiber-reinforced resin composite material and the absorbed energy after the maximum load (propagation energy) thereof at the same time, and is useful as a raw material for producing a fiber-reinforced composite material used in the fields of automobile parts, products for civil engineering and construction, blades for wind power generation, sporting goods, aircraft, ships, robots, cable materials, and the like. 

1. A resin-reinforcing fiber in which a fiber is surface-treated with an epoxidized polydiene resin.
 2. The resin-reinforcing fiber according to claim 1, wherein the fiber is carbon fiber or glass fiber.
 3. A fiber-reinforced resin composite material comprising a resin-reinforcing fiber according to claim 1 and a matrix resin.
 4. The fiber-reinforced resin composite material according to claim 3, wherein the matrix resin is an epoxy thermosetting resin.
 5. A structure comprising a fiber-reinforced resin composite material according to claim
 4. 6. A fiber-reinforced resin composite material comprising a resin-reinforcing fiber according to claim 2 and a matrix resin. 